Transflective liquid crystal display device, method of fabricating the same, and method of using the same

ABSTRACT

A transflective liquid crystal display device includes a liquid crystal panel having a pixel electrode, wherein the pixel electrode includes a first reflective region and a first transmissive region, a patterned reflective panel adjacent to the liquid crystal panel, the patterned reflective panel having a second reflective region and a second transmissive region, and a back light unit adjacent to the patterned reflective panel, wherein the patterned reflective panel is movable along a direction parallel to the liquid crystal panel.

This application is a divisional of U.S. Pat. App. No. 10/268,658 filedOct. 11, 2002,now U.S. Pat. No. 6,750,932. This application also claimsthe benefit of Korean Patent Application No. 2001-63140, filed in Koreaon Oct. 12, 2001, which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) deviceand more particularly, to a transflective liquid crystal display (LCD)device that is used both in a transmissive mode and in a reflectivemode.

2. Discussion of the Related Art

In general, a liquid crystal display (LCD) device includes twosubstrates spaced apart and facing each other, and a liquid crystalmaterial layer interposed between the two substrates. Each of the firstand second substrates includes an electrode, whereby the electrodes ofeach of the first and second substrates face each other. When a voltageis applied to each of the electrodes, an electric field is inducedbetween the electrodes. Accordingly, an alignment of the liquid crystalmolecules of the liquid crystal material layer is changed by the varyingintensity or direction of the induced electric field. Thus, the LCDdevice displays an image by varying transmittance of light through theliquid crystal material layer according to the arrangement of the liquidcrystal molecules. However, since the liquid crystal display (LCD)device is not luminescent, an additional light source is required todisplay images.

The liquid crystal display device may be categorized into two differenttypes depending upon the type of light source used; a transmissive typeand a reflective type. In the transmissive type, a back light ispositioned behind a liquid crystal panel, wherein light incident fromthe back light enters into the liquid crystal panel. Accordingly, anamount of light transmitted through the liquid crystal material layer iscontrolled by the alignment of the liquid crystal molecules. Thus, thesubstrates and the electrodes must be formed of transparent conductivematerials. Since the transmissive liquid crystal display (LCD) deviceuses the back light as a light source, it can display bright images indark surroundings. In addition, the light intensity of the back lightmust be increased since the amount of transmitted light is relativelysmall. Consequently, the transmissive liquid crystal display (LCD)device requires a relatively high power consumption due to the low lightintensity of the back light.

In the reflective type LCD device, ambient sunlight or artificial lightis used as a light source of the LCD device. The ambient light incidentfrom the surroundings is reflected by a reflective plate of the LCDdevice according to the arrangement of the liquid crystal molecules.Since there is no back light, the reflective type LCD device hasconsiderably lower power consumption than the transmissive type LCDdevice. However, the reflective type LCD device may not be suitable foruse in places with low ambient light since an artificial light sourcewould be required.

FIG. 1 is a cross-sectional view of a transflective LCD device accordingto the related art. In FIG. 1, transmissive electrodes 12 are formedalong an inner surface of a first substrate 11 that includes a thin filmtransistor (not shown) electrically connected to each of thetransmissive electrodes 12. Reflective electrodes 13 are formed on thetransmissive electrodes 12, and each has a transmissive hole 13 aexposing a portion of the transmissive electrode 12. A first polarizer14 is arranged along an outer surface of the first substrate 11, therebylinearly polarizing incident light.

A second substrate 21 is spaced apart from and faces the first substrate11, and a color filter layer 22 is formed on an inner surface of thesecond substrate 21. The color filter layer 22 is composed of threesub-color filters of red (R), green (G), and blue (B). Each of thesub-color filters correspond to each of the transmissive electrodes 12.A common electrode 23 is formed on the color filter layer 22, and ismade of a conductive transparent material. A diffusing film 24 and asecond polarizer 25 are subsequently arranged along an outer surface ofthe second substrate 21, wherein a transmission axis of the secondpolarizer 25 is perpendicular to a transmission axis of the firstpolarizer 14. A liquid crystal material layer 30 is disposed between thereflective electrodes 13 and the common electrode 23.

In FIG. 1, a back light unit 40 is disposed beneath the first polarizer14, and is used as a light source during a transmissive mode of thetransflective LCD device. The back light unit 40 includes a light guidepanel 42, a lamp 41, a collimating sheet 43, and a diffusing sheet 44.The light guide panel 42 includes scattering patterns formed along alower surface, thereby changing linear light of the lamp 41 into planelight.

In a transmissive mode, a first light “L1”generated from the back lightunit 40 penetrates into the first polarizer 14 and through the firstsubstrate 11. In addition, the first light “L1” passes through theportion of the transmissive electrode 12 that corresponds to thetransmissive hole 13 a and through the liquid crystal material layer 30.Then, the first light “L1” is transmitted through the common electrode23, the color filter layer 22, the second substrate 21, the diffusingfilm 24, and the second polarizer 25.

In a reflective mode, a second light “L2”incident from ambientsurroundings, such as sunlight or artificial light, passes through thesecond polarizer 25, the diffusing film 24, the second substrate 21, thecolor filter 22, the common electrode 23, and the liquid crystalmaterial layer 30. Then, the second light “L2”is reflected by thereflective electrode 13 and is transmitted back through the liquidcrystal material layer 30, the common electrode 23, the color filter 22,the second substrate 21, the diffusing film 24, and the second polarizer25.

By comparison, the transflective LCD device has lower reflectance thanthe reflective LCD device because of the transmissive hole 13 a formedin the reflective electrode 13. Specifically, in the reflective mode,light incident toward the transmissive hole 13 a is transmitted to theback light unit 40 and is not reflected. In addition, the transflectiveLCD device has lower brightness than the transmissive LCD device in thetransmissive mode since light incident toward the reflective electrode13 from the back light unit 40 is reflected toward the back light unit40.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a transflective liquidcrystal display (LCD) device that substantially obviates one or more ofproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a transflective liquidcrystal display (LCD) device that improves brightness both in atransmissive mode and in a reflective mode.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, atransflective liquid crystal display device includes a liquid crystalpanel having a pixel electrode, wherein the pixel electrode includes afirst reflective region and a first transmissive region, a patternedreflective panel adjacent to the liquid crystal panel, the patternedreflective panel having a second reflective region and a secondtransmissive region, and a back light unit adjacent to the patternedreflective panel, wherein the patterned reflective panel is movablealong a direction parallel to the liquid crystal panel.

In another aspect, a transflective liquid crystal display deviceincludes first and second substrates spaced apart and facing each other,a thin film transistor on an inner surface of the first substrate, afirst passivation layer on the thin film transistor and having a firsttransmissive hole, a transmissive electrode on the first passivationlayer and electrically connected to the thin film transistor, a secondpassivation layer on the transmissive electrode, a reflector on thesecond passivation layer and having a second transmissive hole alignedwith the first transmissive hole, the second transmissive hole defininga first transmissive region and a first reflective region, a colorfilter layer on an inner surface of the second substrate, a commonelectrode on the color filter layer, a liquid crystal material layerbetween the reflector and the common electrode, a first polarizer on anouter surface of the first substrate, a patterned reflective panel overthe first polarizer, the patterned reflective panel having a secondtransmissive region and a second reflective region, a back light unitover the patterned reflective panel, a diffusing film on an outersurface of the second substrate, and a second polarizer on the diffusingfilm, wherein the patterned reflective panel is movable along adirection parallel to the first and second substrates.

In another aspect, a method of fabricating a transflective liquidcrystal display device includes forming a pixel electrode on a liquidcrystal panel, wherein the pixel electrode includes a first reflectiveregion and a first transmissive region, forming a patterned reflectivepanel adjacent to the liquid crystal panel, the patterned reflectivepanel having a second reflective region and a second transmissiveregion, and arranging a back light unit adjacent to the patternedreflective panel, wherein the patterned reflective panel is movablealong a direction parallel to the liquid crystal panel.

In another aspect, a method for changing an operational mode of atransflective liquid crystal display device includes moving a patternedreflective panel along a direction parallel to an adjacent liquidcrystal panel, wherein the liquid crystal panel includes a pixelelectrode having a first reflective region and a first transmissiveregion, and the patterned reflective panel includes a second reflectiveregion and a second transmissive region.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a cross-sectional view of a transflective LCD device accordingto the related art;

FIG. 2 is a cross-sectional view of an exemplary transflective LCDdevice according to the present invention;

FIG. 3 is a plan view of an exemplary patterned reflective panelaccording to the present invention;

FIG. 4 is a cross-sectional view of an exemplary transflective LCDdevice in a transmissive mode according to the present invention;

FIG. 5 is a cross-sectional view of an exemplary transflective LCDdevice in a reflective mode according to the present invention;

FIG. 6 is a plan view of an exemplary array substrate for atransflective LCD device according to the present invention; and

FIG. 7 is a cross-sectional view of the exemplary array substrate alongVII—VII of FIG. 6 according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiment of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 is a cross-sectional view of an exemplary transflective LCDdevice according to the present invention. In FIG. 2, a transflectiveLCD device may have a first substrate 111 and a second substrate 121,wherein the first and second substrates 111 and 121 are spaced apart andface each other. Transmissive electrodes 112 may be formed along aninner surface of the first substrate 111, which may include a thin filmtransistor (not shown) electrically connected to each of thetransmissive electrodes 112. The transmissive electrodes 112 may be madeof a conductive transparent material having a relatively hightransmittance. Reflective electrodes 113 may be formed on each of thetransmissive electrodes 112, wherein each of the reflective electrodes113 may include a transmissive hole 113 a exposing a portion of thetransmissive electrode 112. The reflective electrode 113 may be made ofan conductive opaque material having a relatively high reflectance and arelatively low resistivity. Although the reflective electrodes 113 maybe connected to the transmissive electrodes 112, an insulating layer(not shown) may be positioned between the reflective electrodes 113 andthe underlying transmissive electrodes 112. In addition, thetransmissive electrodes 112 may be formed over the reflective electrodes113.

A first polarizer 114 may be arranged along an outer surface of thefirst substrate 111, thereby linearly polarizing any incident light. Apatterned reflective panel 150 may be arranged between the firstpolarizer 114 and a light source 140. The patterned reflective panel 150may include a reflective portion 151 formed of a blocking layer and atransmissive portion 152 formed of a transparent substrate. Accordingly,the reflective portion 151 and the transmissive portion 152 may belarger than the transmissive hole 113 a. The patterned reflective panel150 may be able to move horizontally along right and left directions oralong front and rear directions. The movement of the patternedreflective panel 150 may be performed in a manual mode or may beperformed in an automatic mode. In either mode, the movement of thepatterned reflective panel 150 may be positioned to provide a desiredimage intensity. Accordingly, light may be reflected both at uppersurfaces and lower surfaces of the reflective portions 151 of thepatterned reflective panel 150.

A color filter layer 122 may be formed along an inner surface of thesecond substrate 121, and may include three sub-color filters of red(R), green (G), and blue (B). Each of the sub-color filters 122 maycorrespond to each of the transmissive electrodes 112. In addition, acommon electrode 123 may be formed on the color filter layer 122, andmay be made of the same conductive transparent material as thetransmissive electrodes 112. Alternatively, the common electrode 123 andthe transmissive electrodes 112 may be made of different conductivetransparent materials.

A diffusing film 124 and a second polarizer 125 may be arranged along anouter surface of the second substrate 121 and may function as ananalyzer, wherein a transmission axis of the second polarizer 125 mayhave an angle of about 90 degrees with a transmission axis of the firstpolarizer 114.

A liquid crystal material layer 130 may be disposed between thereflective electrode 113 and the common electrode 123. In addition,alignment layers may be formed on the reflective electrodes 113 and thecommon electrode 123. Accordingly, molecules of the liquid crystalmaterial layer 130 may be arranged horizontally with respect to thefirst and second substrates 111 and 121 according to the alignmentlayers.

The back light unit 140 may be used as a light source in a transmissivemode in the transflective LCD device. The back light unit 140 mayinclude a light guide panel 142, a lamp 141 located at a side portion ofthe light guide panel 142, a collimating sheet 143, and a diffusingsheet 144 positioned over the light guide 142. The light guide panel 142may include scattering patterns (not shown) formed along the lowersurface, thereby changing linear light emitted from the lamp 141 intoplane light. The scattering patterns (not shown) may be formed by anetching or printing method, for example. Alternatively, the lowersurface of the light guide panel may include multiple regions ofvariable thickness instead of, or in addition to the scatteringpatterns. A reflector (not shown) may be arranged beneath the lightguide panel 142 to prevent light leakage.

FIG. 3 is a plan view of an exemplary patterned reflective panelaccording to the present invention. In FIG. 3, the patterned reflectivepanel 150 may include the reflective portions 151 and the transmissiveportions 152. The patterned reflective panel 150 may be made of atransparent substrate, whereby a blocking layer is positioned upon thetransparent substrate to have a plurality of openings. For example, theblocking layer may correspond to the reflective portions 151 and theopenings may correspond to the transmissive portions 152. Although thetransmissive portions 152 are shown having a square shape, othergeometries may be implemented. For example, rectangular, circular, andhexagonal geometries may be used to form the transmissive portions 152of the patterned reflective panel 150.

FIG. 4 is a cross-sectional view of an exemplary transflective LCDdevice in a transmissive mode according to the present invention. InFIG. 4, the transmissive portion 152 of the patterned reflective panel150 coincides with the transmissive hole 113 a. Accordingly, lightemitted from the back light unit 140 may pass through the transmissiveportion 152 of the patterned reflective panel 150 and may be linearlypolarized by the first polarizer 114. Then, the linearly polarized lightmay pass through the first substrate 111 and the portion of thetransmissive electrode 122 that corresponds to the transmissive hole 113a, and may enter into the liquid crystal material layer 130.Accordingly, transmission of the light may be controlled according to anarrangement of liquid crystal molecules. Finally, a first transmittedlight “T1”may be transmitted through the common electrode 123, the colorfilter layer 122, the second substrate 121, the diffusing film 124, andthe second polarizer 125.

Light emitted from the back light unit 140 and incident upon thereflective portion 151 of the patterned reflective panel 150 may bereflected at the reflective portion 151 of the patterned reflectivepanel 150, and may return back to the back light unit 140. Subsequently,a portion of the light may be reflected to the back light unit 140 andpass through the transmissive portion 152 of the patterned reflectivepanel 150. Thus, a second transmitted light “T2” may be transmittedthrough a same path as the first transmitted light “T1.”

Conversely, ambient light such as sunlight or artificial light maysequentially pass through the second polarizer 125, the diffusing film124, the second substrate 121, the color filter layer 122, the commonelectrode 123, and the liquid crystal material layer 130. Accordingly,the light may be reflected by the reflective electrode 113 andretransmitted back through the liquid crystal material layer 130, thecommon electrode 123, the color filter layer 122, the second substrate121, the diffusing film 124, and the second polarizer 125, and emerge asa reflected light “R.”. Thus, since a total amount of transmitted lightincreases due to the patterned reflective panel 150 and the additionalreflected light “R,” the transflective LCD device may have a relativelyhigher brightness in the transmissive mode.

FIG. 5 is a cross-sectional view of an exemplary transflective LCDdevice in a reflective mode according to the present invention. In FIG.5, the reflective portion 151 of the patterned reflective panel 150corresponds to the transmissive hole 113. Accordingly, ambient lightsuch as sunlight or artificial light may pass through the secondpolarizer 125, thereby linearly polarizing the ambient light. Thelinearly polarized light may pass through the diffusing film 124, thesecond substrate 121, the color filter layer 122, and the commonelectrode 123, and into the liquid crystal material layer 130. Thus, thealignment of the liquid crystal molecules may control the transmissionof the linearly polarized light. Next, the light may be reflected by thereflective electrode 113 and again pass through the liquid crystalmaterial layer 130. Subsequently, the light may be retransmitted throughthe common electrode 123, the color filter layer 122, the secondsubstrate 121, the diffusing film 124, and the second polarizer 125, andemerge as a first reflected light “R1.”

Conversely, a portion of ambient light may pass through the secondpolarizer 125, the diffusing film 124, the second substrate 121, thecolor filter layer 122, the common electrode 123, and the liquid crystalmaterial layer 130. Then, the light may pass through the transmissivehole 113 a, the transmissive electrode 112, the first substrate 111, andthe first polarizer 114, and may be reflected by the reflective portion151 of the patterned reflective panel 150. Accordingly, the light may beretransmitted through the first polarizer 114, the first substrate 111,the transmissive electrode, the transmissive hole 113 a, the liquidcrystal material layer 130, the common electrode 123, the color filterlayer 122, the second substrate 121, the diffusing film 124, and thesecond polarizer 125 to emerge as a second reflected light “R2.” Thus,in the reflective mode of the transflective LCD device, a loss of lightis prevented due to the reflective portion 151 of the patternedreflective panel 150, and the brightness of the transflective LCD deviceincreases.

FIG. 6 is a plan view of an exemplary array substrate for atransflective LCD device according to the present invention, and FIG. 7is a cross-sectional view of the exemplary array substrate along VII—VIIof FIG. 6 according to the present invention. In FIGS. 6 and 7, a gateelectrode 222 may be formed on a transparent substrate 210, and may beconnected to a gate line 221 that extends along a horizontal direction.The transparent substrate 210 may be made of an insulating material suchas glass, and the gate electrode 222 and the gate line 221 may be formedof a conducting material such as a metal. A gate insulator 230 may coverthe gate electrode 222 and the gate line 221, and may be made of siliconnitride (SiNx) or silicon oxide (SiO₂), for example.

An active layer 241 and an ohmic contact layer 251 may be subsequentlyformed on the gate insulator 230, wherein the active layer 241 may bemade of amorphous silicon, for example, and the ohmic contact layer 251may be made of doped amorphous silicon, for example. Next, source anddrain electrodes 262 and 263 may be formed on the ohmic contact layer251, wherein the source electrode 262 may be connected to a data line261 that extends along a vertical direction perpendicular to thehorizontal direction. The data line 261 may cross the gate line 221,thereby defining a pixel region. The ohmic contact layer 251 may lower acontact resistance between the active layer 241 and the source and drainelectrodes 262 and 263.

A first passivation layer 270 may cover the data line 261 and the sourceand drain electrodes 262 and 263, and may include a first contact hole271 and a first transmissive hole 272. The first passivation layer 270may be made of a benzocyclobutene (BCB) or a photosensitive acrylicresin, for example. The first contact hole 271 may expose a portion ofthe drain electrode 263 and the first transmissive hole 272 may expose aportion of the transparent substrate 210 through the gate insulator 230.Alternatively, the gate insulator 230 may be not etched such that thefirst transmissive hole 272 may be formed only through the firstpassivation layer 270. The first transmissive hole 272 may result inincreasing a thickness of a liquid crystal material layer (not shown) ina transmissive region. Accordingly, a thickness of the liquid crystalmaterial layer in a reflective region may be relatively thinner, therebyoptimizing an optical characteristic of a transmissive mode with anoptical characteristic of a reflective mode, simultaneously.

A transmissive electrode 280 may be formed on the first passivationlayer 270, and positioned in the pixel region. The transmissiveelectrode 280 may be connected to the drain electrode 263 through thefirst contact hole 271. The transmissive electrode 280 may be made of aconductive transparent material such as indium-tin-oxide (ITO) andindium-zinc-oxide (IZO), for example.

A second passivation layer 290 may be formed on the transmissiveelectrode 280, and may include a second contact hole 291 that exposes aportion of the transparent electrode 270 that corresponds to the firstcontact hole 271. The second passivation layer 290 may be made ofsilicon nitride (SiNx) and silicon oxide (SiO₂), for example.

A reflective electrode 300 may be formed on the second passivation layer290, and may be connected to the transmissive electrode 280 through thesecond contact hole 291, thereby functioning as a reflector.Alternatively, the reflective electrode 300 may be formed beneath thetransmissive electrode 280 and may not be connected to the transmissiveelectrode 280. The reflector 300 may include a second transmissive hole302 that exposes a portion of the transmissive electrode 280 thatcorresponds to the first transmissive hole 272.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the fabrication andapplication of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

1. A transflective liquid crystal display device, comprising: first andsecond substrates spaced apart and facing each other; a thin filmtransistor on an inner surface of the first substrate; a firstpassivation layer on the thin film transistor and having a firsttransmissive hole; a transmissive electrode on the first passivationlayer and electrically connected to the thin film transistor; a secondpassivation layer on the transmissive electrode; a reflector on thesecond passivation layer and having a second transmissive hole alignedwith the first transmissive hole, the second transmissive hole defininga first transmissive region and a first reflective region; a colorfilter layer on an inner surface of the second substrate; a commonelectrode on the color filter layer; a liquid crystal material layerbetween the reflector and the common electrode; a first polarizer on anouter surface of the first substrate; a patterned reflective panel overthe first polarizer, the patterned reflective panel having a secondtransmissive region and a second reflective region; a back light unitover the patterned reflective panel; a diffusing film on an outersurface of the second substrate; and a second polarizer on the diffusingfilm, wherein the patterned reflective panel is movable along adirection parallel to the first and second substrates.
 2. The deviceaccording to claim 1, wherein the second transmissive region has an arealarger than the second transmissive hole.
 3. The device according toclaim 1, wherein the second reflective region has an area larger thanthe second transmissive hole.
 4. The device according to claim 1,wherein the first reflective region overlaps the second reflectiveregion and the first transmissive region overlaps the secondtransmissive region.
 5. The device according to claim 1, wherein thefirst reflective region overlaps the second transmissive region and thefirst transmissive region overlaps the second reflective region.
 6. Thedevice according to claim 1, wherein the reflector is electricallyconnected to the transmissive electrode.
 7. The device according toclaim 1, wherein the first passivation layer includes one ofbenzocyclobutene (BCB) and acrylic resin.